The present disclosure relates generally to the field of engine generators. More particularly, the present disclosure relates to variable speed engine generator. According to one exemplary embodiment a system including a diesel generator set is disclosed.
Engine generators generally include a prime mover (e.g., engine), electrical generator 40, and various controllers and circuitry. Collectively, the components of an engine generator are often referred to as a generator set, gen-set, or genset. The prime mover is configured to create mechanical energy and is mechanically linked to the electrical generator to transfer the mechanical energy to the electrical generator. The electrical generator is configured to convert the mechanical energy from the prime mover into electrical energy, such as alternating current (AC) electrical power. Other controllers may, for example, include a system controller (i.e., for the engine generator or plurality of engine generators used together) and an engine controller (i.e., to control the prime mover).
As shown in FIG. 1, conventional engine generators are configured for the engine to operate at fixed speeds, often according to the frequency of AC current used in particular regions. For example, an engine-generator set 100 may produce AC current at 50 Hz for use in the United Kingdom with the engine set to operate at 1500 or 3000 RPM. The engine speed is set by an input 240 to the engine controller or governor 220. An engine-generator for use in the United States may produce AC current at 60 Hz and have an engine set to operate at 1800 or 3600 RPM. The fixed speeds of the prime mover (engine) 200 ensure generally constant frequency output.
Variable speed engine generators are configured for the prime mover to operate through a range of speeds. The generator set 300 includes an output converter to adjust the output voltage. The output may be rectified using conditioning circuitry to convert AC power into DC power having generally constant voltage. The DC power output from the rectifier may then be used to power DC-powered electronic devices or be converted by other circuitry into AC power.
One difficulty associated with engine generators, whether fixed or variable speed, is their ability to respond to transient (i.e., changing) load conditions, such as when an electrical load is started or where there is prompt increase in power requirement. The additional load placed on the generator 300 causes a corresponding drop in the voltage produced by the electrical generator. The voltage regulator 350, for example in a wound-field generator, receives inputs related to the sensed voltage 370 and the desired voltage setting 380 and attempts to regulate voltage by increasing the excitation (i.e., field current 360) of the electrical generator. The increased excitation causes a corresponding increase in the counter torque applied to the engine 200, thereby increasing load on the engine 200 and reducing engine speed. In response to an input related to the change of speed 210, the engine controller 220 and/or the system controller may call for increased output from the engine to match the electrical load drawn from the electrical generator, such as by adjusting fuel delivery 230 to the engine to restore or maintain engine speed. However, because engine speed is a lagging indicator of electrical load, the electrical output 340 of the generator 300 may fluctuate causing inconsistent and inefficient power delivery to attached devices.
Another difficulty associated with responding to transient conditions is the possibility of engine stalling. In order to meet stringent emission control standards, engines are controlled so that fuel delivery is restricted in certain situations. For example, the engine and/or system controller may call for more fuel to create additional torque, but the emissions control program of the engine controller may prevent delivery of fuel to the engine so as to prevent creation of harmful pollutants, such as particulate matter and NOx. More particularly, for engines utilizing turbochargers, the engine controller may limit fuel injection until boost pressure is built up in the intake manifold. Meanwhile, while increased fuel delivery is delayed, counter torque from the electrical generator continues to increase and may ultimately overcome engine torque and cause the engine to stall. Controls may also limit fuel delivery to prevent engine damage or fuel waste, and fuel delivery may be limited by physical parameters of the engine design itself.
Accordingly, it would be advantageous to provide an engine generator and control system that more quickly respond to increased electrical load conditions for consistent power delivery and to prevent engine stalling.